The content of carbon and its stability in forest soils in the vicinity of roadways has not yet been thoroughly investigated. The aim of this work was to investigate the content of soil organic carbon in forest soils, in relation to soil cation exchange properties in the vicinity of a roadway. We assumed that input of sodium, originating from the winter road de−icing, reduces the concentration of other cations and therefore, modifies relations between ions in soil cation exchange capacity. Changes to these relations may potentially influence the stability and accumulation of soil carbon. We selected four study sites adjacent to the S7 roadway in Poland. Data confirmed that soil in the close vicinity to the roadway had an enhanced concentration of sodium, magnesium and calcium. We also found increased level of carbon accumulation at 2−12 m distance from the forest edge. Increased carbon content, particularly of the light fraction, originated from roots and aboveground parts of the forest understory layer, observed as much better developed at the forest edge than further into the forest. Stable fraction and dissolved organic carbon were mostly related to the soil aluminum and iron contents, which were also increased closer to the roadway.

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